Drive device

ABSTRACT

A drive device that includes an alternating-current rotary electric machine in which currents of a plurality of phases flow; an inverter that includes switching element units for respective phases corresponding to the respective phases, and that is connected between a direct-current power supply and the alternating-current rotary electric machine and performs conversion between a direct current and an alternating current; and shunt resistors that detect currents flowing in the respective switching element units for the corresponding phases between the direct-current power supply and the switching element units for the respective phases

BACKGROUND

The present disclosure relates to a drive device including a rotaryelectric machine and an inverter connected between the rotary electricmachine and a direct-current power supply.

A device disclosed in Japanese Patent Application Publication No.2007-166803 is known as such a drive device as described above. Tocontrol drive of a rotary electric machine (motor-generators MG1 andMG2) in such a device, the device needs to be provided with a currentsensor for detecting a current flowing in a stator coil of each phase.The conventional current sensor used in the drive device generally usesa Hall element as shown in Japanese Patent Application Publication No.2007-166803. The sensor using the Hall element has relatively stabletemperature characteristics and can accurately detect the current, andhence, is often used to enable accurate drive control of the rotaryelectric machine in the drive device likely to be subjected to a hightemperature environment. The sensor using the Hall element is, however,generally expensive, thereby contributing to an increase in cost.

In the case of, for example, electrical appliances, such as an airconditioner, techniques are known in which a shunt resistor provided inan inverter circuit is used to detect the current flowing in the statorcoil of each phase of the rotary electric machine (Japanese PatentApplication Publication No. 2011-125130, Japanese Patent ApplicationPublication No. 2005-151790 and Japanese Patent Application PublicationNo. 2005-192358). The shunt resistor is inexpensive, and hence, theproduct cost can be lower than that in the case of structuring therotary electric machine such that the current is detected by the sensorusing the Hall element.

The shunt resistor is, however, lower in current detection accuracy andmore susceptible to ambient temperature than the sensor using the Hallelement. This may prevent desired accuracy from being ensured for thedrive control of the rotary electric machine (such as themotor-generators MG1 and MG2 in Japanese Patent Application PublicationNo. 2007-166803) when the shunt resistor is used to simply reduce theproduct cost. In particular, in view of the fact that the installationenvironment of the drive device tends to be of considerably highertemperature than the installation environment of general electricalappliances, using the shunt resistor is liable to reduce accuracy ofcontrolling the rotary electric machine. Hence, in the case of using theshunt resistor for current detection in the drive device, sufficientconsideration is necessary as to in what form the shunt resistor isused.

SUMMARY

In view of the above, the product cost of the drive device including therotary electric machine and the inverter is desired to be lower whilegiving a smaller influence on the accuracy of controlling the rotaryelectric machine.

A drive device according to an exemplary aspect of the presentdisclosure includes an alternating-current rotary electric machine inwhich currents of a plurality of phases flow; an inverter that includesswitching element units for respective phases corresponding to therespective phases, and that is connected between a direct-current powersupply and the alternating-current rotary electric machine and performsconversion between a direct current and an alternating current; andshunt resistors that detect currents flowing in the respective switchingelement units for the corresponding phases between the direct-currentpower supply and the switching element units for the respective phases,wherein the alternating-current rotary electric machine is drivinglyconnected to a rotating body provided independent of wheels, and theshunt resistors are arranged in a driving force source roomaccommodating a driving force source of the wheels.

In the present application, the expression “drivingly connected” refersto a state in which two rotational elements are connected to each otherso as to be capable of transmitting driving force (synonymous withtorque) therebetween. This concept includes a state in which the tworotational elements are connected so as to rotate together with eachother and a state in which the two rotational elements are connected soas to transmit the driving force therebetween via one or moretransmitting members. Such transmitting members include various members(such as shafts, gear mechanisms, and belts) that transmit rotation atthe same speed or at a changed speed, and may include engagement devices(such as friction engagement devices and meshing engagement devices)that selectively transmit the rotation and the driving force.

The term “alternating-current rotary electric machine” represents arotary electric machine driven by alternating-current power. The term“rotary electric machine” is used as a concept including all of a motor(electric motor), a generator (electric generator), and amotor-generator that carries out both the functions of a motor and agenerator as necessity.

The expression “independent of wheels” means that a transmission path ofthe driving force is independent of the wheels, so that the rotationaldriving force of the wheels is not transmitted to the transmission path.

With this characteristic feature, the shunt resistors detect thecurrents flowing in the respective switching element units for thecorresponding phases included in the inverter, so that the product costcan be lower than that in the case in which sensors using Hall elementsdetect the currents. The alternating-current rotary electric machinecontrolled by the inverter is drivingly connected to the rotating body(such as a rotor of, for example, an oil pump, a water pump, or an airconditioner compressor) provided independent of the wheels. For thisreason, the alternating-current rotary electric machine is oftenrequired to have control accuracy that is not as high as that of, forexample, a rotary electric machine for driving the wheels (wheel drivingrotary electric machine). Accordingly, the control accuracy of thealternating-current rotary electric machine can be relatively lessaffected by using the shunt resistors for the current detection. Inparticular, the control accuracy of the alternating-current rotaryelectric machine can be relatively less affected when the shuntresistors are arranged in the driving force source room and placed undera high-temperature environment.

The following describes preferable exemplary aspects of the presentdisclosure.

As an aspect of the present disclosure, the drive device preferablyfurther includes a drive transmission device that operates withhydraulic pressure supplied thereto and controls a transmission state ofdriving force from the driving force source to the wheels, and therotating body is preferably a rotor of an electric pump that dischargesoil supplied to the drive transmission device.

This structure allows the oil discharged by the electric pump to besupplied to the drive transmission device so as to appropriately controlthe transmission state of the driving force from the driving forcesource to the wheels. The drive of the rotor of the electric pumpdrivingly connected to the alternating-current rotary electric machineis controlled while detecting the currents flowing in thealternating-current rotary electric machine using the shunt resistors,so that the state of the drive transmission device can be relativelyaccurately controlled. The inverter controls the alternating-currentrotary electric machine for driving the rotor of the electric pump, sothat the state of the drive transmission device can be relativelyaccurately controlled, and the currents can be detected using low-costshunt resistors so as to reduce the product cost.

As another aspect of the present disclosure, the alternating-currentrotary electric machine is preferably structured such that N-phasecurrents (N is a natural number of 2 or more) flow therein; a positiveelectrode of the direct-current power supply is preferably connected tothe switching element units for the respective phases through a commonpositive line common to the N switching element units for the respectivephases and N positive branch lines branching from the common positiveline and connected to the respective switching element units for therespective phases, and a negative electrode of the direct-current powersupply is preferably connected to the switching element units for therespective phases through a common negative line common to the Nswitching element units for the respective phases and N negative branchlines branching from the common negative line and connected to therespective switching element units for the respective phases; and theshunt resistors are preferably provided in respective N or (N−1)negative branch lines.

This structure allows a ground electric potential to be used as areference electric potential by taking advantage of the normal practiceof connecting the negative electrode of the direct-current power supplyto a ground. As a result, unlike, for example, a structure in which theshunt resistors are provided in the positive branch lines, installationof a circuit for generating the reference electric potential can beomitted, so that the device can be reduced in size. The currents flowingin the respective phases of the alternating-current rotary electricmachine can be appropriately detected using the N shunt resistors, orusing the (N−1) shunt resistors and utilizing the principle that the sumof instantaneous values of the currents of the respective phases iszero.

In the case of detecting the currents flowing in the respective phasesof the alternating-current rotary electric machine using the shuntresistors, a zero point offset needs to be corrected. For devices, suchas electrical appliances, subjected to relatively small temperaturechanges in the use environment, such an offset correction is normallyperformed only at the start of the devices. Considering applications tothe drive device, however, the ambient temperature greatly fluctuates,so that the current detection accuracy may be reduced if the offsetcorrection is performed only at the start of the device.

In view of this, as still another aspect of the present disclosure, thedrive device preferably further includes an inverter control device thatcontrols drive of the inverter. In the drive device, each of theswitching element units for the respective phases preferably includes anupper switching element and a lower switching element, the upperswitching element being provided closer to the positive electrode of thedirect-current power supply than a connection part of the switchingelement unit to the alternating-current rotary electric machine, thelower switching element being provided closer to the negative electrodeof the direct-current power supply than the connection part; each of theshunt resistors is preferably provided so as to detect a current flowingin the lower switching element of corresponding one of the switchingelement units for the respective phases; and the inverter control devicepreferably controls the alternating-current rotary electric machine byPWM control by individually controlling switching of the upper switchingelement and the lower switching element of each of the switching elementunits for the respective phases, preferably performs a current detectionprocess of detecting the currents of respective phases flowing in thealternating-current rotary electric machine based on an electricpotential difference between both ends of each of the shunt resistorsduring a lower full-on period in which the lower switching elements ofthe switching element units for the respective phases are all ON, andpreferably determines an offset correction amount at a zero point in thecurrent detection process based on the electric potential differencebetween both ends of each of the shunt resistors during a lower full-offperiod in which the lower switching elements of the switching elementunits for the respective phases are all OFF.

This structure allows simultaneous detection of the currents of therespective phases by utilizing the phenomenon that the current of eachphase flows in the lower switching element for the phase during thelower full-on period in which the lower switching elements for therespective phases are all ON. During the lower full-off period in whichthe lower switching elements for the respective phases are all OFF, thecurrent of each phase flows in the upper switching element for thephase, and does not theoretically flow in the lower switching element.As a result, the offset correction amount at the zero point in thecurrent detection process can be appropriately determined by utilizingthe currents detected by the shunt resistors during the lower full-offperiod in which the current values should be zero in principle. Theoffset correction can be repeatedly performed by determining the offsetcorrection amount during the lower full-off period repeatedly appearingduring the drive control of the alternating-current rotary electricmachine. Thus, the drive device can deal with the fluctuation in theambient temperature. As a result, the detection accuracy in the currentdetection process can be increased.

As still another aspect of the present disclosure, the inverter controldevice preferably individually determines the offset correction amountfor each of the shunt resistors in each of a plurality of dividedperiods defined by dividing an electrical angle period of thealternating-current rotary electric machine.

A study conducted by the inventors of the present disclosure has foundthat the amounts of the currents detected by the shunt resistors duringthe lower full-off period are not uniform, but the amounts of thecurrents of the respective phases flowing in the alternating-currentrotary electric machine are correlated with one another. With thisstructure, the offset correction amount in each of the divided periodsis individually determined, so that the appropriate offset correctionamount can be determined in accordance with the amount of the current ofeach of the phases flowing in the alternating-current rotary electricmachine. As a result, the detection accuracy in the current detectionprocess can be further increased.

When the structure is employed in which the currents of the respectivephases are simultaneously detected during the lower full-on period asdescribed above, the lower full-on period of a predetermined time orlonger is preferably secured to ensure correctness of the currentdetection process. For that purpose, for example, the carrier frequencyin the PWM control may be set in advance to a frequency at which thelower full-on period of the certain time or longer can be secured.However, uniformly reducing the carrier frequency may degradecontrollability of the alternating-current rotary electric machine, andmay generate noise in some cases depending on the relation with theaudible range. For this reason, the inverter control device ispreferably structured to secure the lower full-on period of the certaintime or longer while restraining these problems from occurring.

In view of this, as still another aspect of the present disclosure, thedrive device preferably further includes an inverter control device thatcontrols drive of the inverter. In the drive device, each of theswitching element units for the respective phases preferably includes anupper switching element and a lower switching element, the upperswitching element being provided closer to the positive electrode of thedirect-current power supply than a connection part of the switchingelement unit to the alternating-current rotary electric machine, thelower switching element being provided closer to the negative electrodeof the direct-current power supply than the connection part; each of theshunt resistors is preferably provided so as to detect a current flowingin the lower switching element of corresponding one of the switchingelement units for the respective phases; and the inverter control devicepreferably controls the alternating-current rotary electric machine bythe PWM control by individually controlling switching of the upperswitching element and the lower switching element of each of theswitching element units for the respective phases, preferably performs acurrent detection process of detecting the currents of the respectivephases flowing in the alternating-current rotary electric machine basedon an electric potential difference between both ends of each of theshunt resistors during a lower full-on period in which the lowerswitching elements of the switching element units for the respectivephases are all ON, and preferably reduces a carrier frequency in the PWMcontrol when the lower full-on period is shorter than a predeterminedreference time.

This structure allows simultaneous detection of the currents of therespective phases by utilizing the phenomenon that the current of eachphase flows in the lower switching element for the phase during thelower full-on period in which the lower switching elements for therespective phases are all ON. At this time, if the lower full-on periodis shorter than the predetermined time, the correctness of the currentdetection process may be reduced. To solve this problem, the carrierfrequency in the PWM control is made dynamically changeable, and isreduced if the lower full-on period is shorter than the predeterminedreference time. This configuration can increase the duration time of theON state of each of the lower switching elements for the respectivephases while keeping a duty ratio constant. As a result, the lowerfull-on period can be increased, so that the correctness of the currentdetection process can be easily ensured.

As still another aspect of the present disclosure, the inverter controldevice is preferably structured such that the carrier frequency can bechanged in a continuous manner or a step-like manner, and when the lowerfull-on period is shorter than the reference time, preferably reducesthe carrier frequency to the highest frequency in a range of thechangeable carrier frequency at which the lower full-on period is notshorter than the reference time.

With this structure, the lower full-on period can be equal to or longerthan the reference time, so that the correctness of the currentdetection process can be ensured. This structure can also reduce theamount of reduction in the carrier frequency to as small a level aspossible, and can thereby reduce the degradation in controllability andthe generation of noise of the alternating-current rotary electricmachine.

As still another aspect of the present disclosure, the drive devicepreferably further includes an inverter control device that controlsdrive of the inverter. In the drive device, each of the switchingelement units for the respective phases preferably includes an upperswitching element and a lower switching element, the upper switchingelement being provided closer to the positive electrode of thedirect-current power supply than a connection part of the switchingelement unit to the alternating-current rotary electric machine, thelower switching element being provided closer to the negative electrodeof the direct-current power supply than the connection part; each of theshunt resistors is preferably provided so as to detect a current flowingin the lower switching element of corresponding one of the switchingelement units for the respective phases; and the inverter control devicepreferably controls the alternating-current rotary electric machine byPWM control by individually controlling switching of the upper switchingelement and the lower switching element of each of the switching elementunits for the respective phases based on alternating-current voltagecommands that are commands for alternating-current voltages of aplurality of phases, preferably performs a current detection process ofdetecting the currents of respective phases flowing in thealternating-current rotary electric machine based on an electricpotential difference between both ends of each of the shunt resistorsduring a lower full-on period in which the lower switching elements ofthe switching element units for the respective phases are all ON, andpreferably reduces a modulation factor representing a ratio of aneffective value of the alternating-current voltage commands to a voltageon the direct-current side of the inverter when the lower full-on periodis shorter than a predetermined reference time.

This structure allows simultaneous detection of the currents of therespective phases by utilizing the phenomenon that the current of eachphase flows in the lower switching element for the phase during thelower full-on period in which the lower switching elements for therespective phases are all ON. At this time, if the lower full-on periodis shorter than the predetermined time, the correctness of the currentdetection process may be reduced. To solve this problem, if the lowerfull-on period is shorter than the predetermined reference time, themodulation factor is reduced by changing the voltage on thedirect-current side of the inverter or the alternating-current voltagecommands. This configuration can increase the duration time of the ONstate of each of the lower switching elements for the respective phases.As a result, the lower full-on period can be increased, so that thecorrectness of the current detection process can be easily ensured.

As still another aspect of the present disclosure, the inverter controldevice is preferably structured to control the alternating-currentrotary electric machine by current vector control, and preferablyreduces the modulation factor by performing field-weakening control toadjust the alternating-current voltage commands so as to change amagnetic field generated by stator coils of the alternating-currentrotary electric machine to have the direction of weakening a magneticfield flux of a rotor.

With this structure, the modulation factor can be effectively reduced byperforming the field-weakening control to reduce the alternating-currentvoltage commands and the effective value thereof for causing thealternating-current rotary electric machine to generate required torque.The required output torque of the alternating-current rotary electricmachine can be ensured while increasing the lower full-on period byreducing the modulation factor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a schematic structure of a drivedevice.

FIG. 2 is an exploded perspective view of the drive device.

FIG. 3 is a circuit diagram of an inverter device.

FIG. 4 is a block diagram of an inverter control device.

FIG. 5 is a schematic diagram showing an example of control signals.

FIG. 6 is a schematic diagram showing an example of a flow of a currentduring an active vector period.

FIG. 7 is a schematic diagram showing the flow of the current during alower full-on period.

FIG. 8 is a schematic diagram showing the flow of the current during alower full-off period.

FIG. 9 is a waveform diagram showing a detection method of an actualcurrent flowing in a stator coil.

FIG. 10 is a schematic diagram showing an adjustment method during thelower full-on period based on a carrier frequency.

FIG. 11 is a diagram showing a change in a current command value byfield-weakening control.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment according to the present disclosure will be described withreference to the accompanying drawings. A drive device 1 according tothe present disclosure is a vehicle drive device (hybrid vehicle drivedevice) for driving a vehicle (hybrid vehicle) provided with both aninternal combustion engine E and a rotary electric machine MG as drivingforce sources of wheels W. Specifically, the drive device 1 isstructured as a drive device for a one-motor parallel type hybridvehicle.

1. Schematic Structure of Drive Device

As shown in FIG. 1, the drive device 1 includes an input shaft I as aninput member drivingly connected to the internal combustion engine E,output shafts O as output members drivingly connected to the wheels W,the rotary electric machine MG, and a transmission device TM. In thepresent embodiment, the drive device 1 includes an engagement device CL,a gear mechanism G, and a differential gear unit DF. The engagementdevice CL, the rotary electric machine MG, the transmission device TM,the gear mechanism G, and the differential gear unit DF are provided ina power transmission path connecting the input shaft I to the outputshafts O. These components are provided in the order listed above fromthe side of the input shaft I. These components are accommodated in acase (drive device case) 2. In the present embodiment, the internalcombustion engine E and the drive device 1 are disposed in a drivingforce source room (engine room, in the present example) Q provided inthe vehicle.

The input shaft I, the rotary electric machine MG, and the transmissiondevice TM are coaxially disposed. In the present embodiment, a directionparallel to a rotation center axis common to the components listed aboveis defined as “axial direction”. The input shaft I, the rotary electricmachine MG, and the transmission device TM are disposed along the axialdirection in the order listed above from the side of the internalcombustion engine E. Each of the gear mechanism G and the differentialgear unit DF is disposed such that the rotation center axis thereof isparallel to the axial direction and does not coincide with the rotationcenter axis of the input shaft I and the coaxial components. The drivedevice 1 having such a multi-axis structure (three-axis structure, inthe present example) is suitable, for example, for the case of beingmounted on a front-engine front-drive (FF) vehicle.

As shown in FIG. 1, the input shaft (drive device input shaft) I isdrivingly connected to the internal combustion engine E. The internalcombustion engine E is a motor (such as a gasoline engine or a dieselengine) that outputs mechanical power by being driven by combustion offuel in the engine. In the present embodiment, the input shaft I isdrivingly connected to an output shaft (such as a crankshaft) of theinternal combustion engine E.

The engagement device CL is provided in the power transmission pathconnecting the input shaft I to the rotary electric machine MG. Theengagement device CL selectively drivingly connects the input shaft I(internal combustion engine E) to the rotary electric machine MG. Theengagement device CL functions as an internal combustion enginedisconnection engagement device for disconnecting the internalcombustion engine E from the wheels W. The engagement device CL isstructured as a hydraulically driven friction engagement device.

The rotary electric machine MG includes a stator St fixed to the case 2and a rotor Ro rotatably supported radially inside the stator St. Therotary electric machine MG can function as a motor (electric motor) forgenerating mechanical power using electric power supplied thereto, andas a generator (electric generator) for generating electric power usingmechanical power acted thereon. The rotary electric machine MG iselectrically connected to an electric storage device B (such as abattery or a capacitor) via a first inverter 30. The rotary electricmachine MG performs power running using the electric power supplied fromthe electric storage device B, or generates the electric power fromtorque of the internal combustion engine E or an inertial force of thevehicle and supplies the generated electric power to the electricstorage device B to charge it. The rotary electric machine MG functionsas a “wheel driving rotary electric machine” that outputs driving forcetransmitted to the wheels W. The rotor Ro in the rotary electric machineMG is drivingly connected to an intermediate shaft M so as to rotatetogether with the intermediate shaft M. The intermediate shaft M servesas an input shaft (transmission input shaft) of the transmission deviceTM.

In the present embodiment, the transmission device TM is an automaticstepped transmission device that includes a plurality of gear mechanismsand a plurality of engagement devices for shifting, and can switchbetween a plurality of shift speeds with different speed ratios.Examples of the transmission device TM may include, but are not limitedto, an automatic continuously variable transmission device that cansteplessly change the speed ratio, a manual stepped transmission devicethat includes a plurality of switchable shift speeds with differentspeed ratios, and a constant-speed transmission device that includes asingle shift speed with a fixed speed ratio. The transmission device TMchanges the rotational speed of the intermediate shaft M and convertsthe torque transmitted to the intermediate shaft M in accordance withthe speed ratio at each time, and transmits the changed rotational speedand the converted torque to a transmission output gear Go of thetransmission device TM.

The transmission output gear Go is drivingly connected to the gearmechanism (counter gear mechanism) C. The gear mechanism G includes afirst gear G1 and a second gear G2, each provided on a common shaftmember. The first gear G1 meshes with the transmission output gear Go ofthe transmission device TM. The second gear G2 meshes with adifferential input gear Gi of the differential gear unit DF.

The differential gear unit (output differential gear unit) DF isdrivingly connected to the wheels W via the output shafts O. Thedifferential gear unit DF includes the differential input gear Gi and adifferential body (body of the differential gear unit DF) connected tothe differential input gear Gi. In the differential body, thedifferential gear unit DF distributes and transmits the rotation and thetorque supplied to the differential input gear Gi to the two, left andright, output shafts O (that is, the two, left and right, wheels W). Inthis way, the drive device 1 can transmit the torque of at least one ofthe internal combustion engine E and the rotary electric machine MG tothe wheels W to drive the vehicle.

The drive device 1 includes a mechanical pump (not shown) drivinglyconnected to the intermediate shaft M. The mechanical pump uses thetorque of the internal combustion engine E or the rotary electricmachine MG serving as a driving force source to discharge oil while atleast one of the internal combustion engine E and the rotary electricmachine MG is rotating. In the present embodiment, the drive device 1further includes an electric pump EP driven by a pump motor PM providedindependent of the wheels W. In other words, the pump motor PM isdrivingly connected to a rotor of the electric pump EP providedindependent of the wheels W. In the present embodiment, the pump motorPM corresponds to an “alternating-current rotary electric machine” inthe present disclosure. The rotor of the electric pump EP corresponds toa “rotating body” in the present disclosure. The pump motor PM iselectrically connected to the electric storage device B via a secondinverter 40.

In the present embodiment, the common electric storage device B servingas a source of electrical power drives the rotary electric machine MGcontrolled by the first inverter 30 and the pump motor PM controlled bythe second inverter 40. The voltage (for example, 100 V to 400 V) of theelectric storage device B is higher than the voltage (for example, 12 Vto 24 V) of a battery for accessories serving as a source of electricalpower for accessories, such as a compressor of an air conditioner and anaudio instrument, provided on the vehicle.

The electric pump EP discharges oil using the torque of the pump motorPM in a rotating state. The oil discharged from at least one of themechanical pump and the electric pump EP is used for generatinghydraulic pressure supplied to a hydraulic servomechanism (not shown) ofthe transmission device TM to control the state of engagement of theengagement devices for shifting included in the transmission device TM.The transmission device TM operates with the hydraulic pressure suppliedthereto, and controls the transmission state of the driving force fromat least one of the internal combustion engine E and the rotary electricmachine MG to the wheels W. In the present embodiment, the transmissiondevice TM corresponds to a “drive transmission device” in the presentdisclosure.

The oil discharged from at least one of the mechanical pump and theelectric pump EP is also used, for example, for cooling the rotaryelectric machine MG, and for lubricating various parts. Including theelectric pump EP allows the present embodiment to supply the oil to theengagement devices for shifting to establish engagement states thereofeven while the internal combustion engine E is stopped, so that thevehicle can be appropriately started. The drive device 1 according tothe present embodiment can be suitably used as a drive device for ahybrid vehicle having an engine start-stop function.

As shown in FIG. 2, the case 2 includes an outer peripheral wall 21formed in a deformed cylindrical shape along the outline of thetransmission device TM, the gear mechanism G, and the differential gearunit DF, and also includes a pair of projecting walls 22 oppositelyarranged so as to project outward from the outer peripheral wall 21. Aspace defined by the outer peripheral wall 21 and the pair of projectingwalls 22 forms an inverter housing P. The inverter housing Paccommodates the first inverter 30 and the second inverter 40constituting an inverter device 3. In this way, the first inverter 30and the second inverter 40 are integrally fixed to the case 2 (outerperipheral wall 21).

In other words, the first inverter 30 and the second inverter 40 aredirectly fixed to and integrated with the case 2 not via an invertercase for accommodating the first inverter 30 and the second inverter 40.That is, the drive device 1 according to the present embodiment employsan “inverter-caseless” structure. Such an inverter-caseless structureneed not be provided with a dedicated inverter case, and also need notbe provided with a fixing seat for fixing the inverter case to the case2. This structure can reduce cost through reduction in the number ofcomponents. The overall size of the device can also be reduced.

As shown in FIG. 2, the case 2 in the present embodiment includes acolumnar or planar beam part 23 connecting the pair of projecting walls22 to each other. The case 2 also includes a thick plate-like isolationwall (not shown) extending from the outer peripheral wall 21 toward thebeam part 23. The isolation wall divides the inverter housing P into afirst housing portion P1 and a second housing portion P2. The firsthousing portion P1 accommodates the first and the second inverters 30and 40. The second housing portion P2 accommodates a capacitor Cconstituting the inverter device 3. In that state, the first housingportion P1 is covered with a first cover 26, and the second housingportion P2 is covered with a second cover 27. The first inverter 30 andthe second inverter 40, together with the case 2 of the drive device 1,are disposed in the driving force source room Q (refer to FIG. 1).

2. Schematic Structure of Inverter Device

The inverter device 3 performs conversion between direct-current powerand alternating-current power. The inverter device 3 includes the firstinverter 30 connected between the electric storage device B and therotary electric machine MG, and performing the power conversion betweena direct current and an alternating current, and also includes thesecond inverter 40 connected between the electric storage device B andthe pump motor PM, and performing the power conversion between a directcurrent and an alternating current. In the present embodiment, the firstinverter 30 and the second inverter 40 share the electric storage deviceB, and also share the capacitor C for smoothing the direct-current power(reducing fluctuations in the direct-current power). Each of the rotaryelectric machine MG and the pump motor PM is structured as a rotaryelectric machine driven by a multi-phase alternating current(three-phase alternating current, in the present example), beingstructured to pass currents of three phases (U-phase, V-phase, andW-phase).

As shown in FIG. 3, the capacitor C is connected between a positiveelectrode Bp side and a negative electrode Bn side (for example, theground side) of the electric storage device B serving as adirect-current power supply, through a pair of common positive line Lp0and common negative line Ln0. Switching element units 31 for therespective phases constituting the first inverter 30 are connected inparallel with one another between the common positive line Lp0 and thecommon negative line Ln0. Specifically, the switching element units 31are respectively connected between three positive branch lines Lp1 toLp3 branching from the common positive line Lp0 and three negativebranch lines Ln1 to Ln3 branching from the common negative line Ln0. Theswitching element units 31 correspond to the three respective phases(U-phase, V-phase, and W-phase) of stator coils of the rotary electricmachine MG (stator St).

Each of the switching element units 31 includes an upper switchingelement 32 provided on the positive electrode Bp side of the electricstorage device B with respect to a connection part of the switchingelement unit 31 and the rotary electric machine MG, and also includes alower switching element 32 provided on the negative electrode Bn side ofthe electric storage device B with respect to the aforementionedconnection part. In other words, the first inverter 30 includes upperswitching elements 32 a to 32 c, each connected to the common positiveline Lp0, and lower switching elements 32 d to 32 f, each connected tothe common negative line Ln0. A set of two parallel-connected switchingelements 32 may be used instead of the switching elements 32 in theexample of FIG. 3. While the present example uses an insulated gatebipolar transistor (IGBT) as the switching element 32, for example, ametal-oxide-semiconductor field-effect transistor (MOSFET) may be usedas the switching element 32.

The collectors of the upper switching elements 32 a, 32 b, and 32 c ofthe respective phases are connected to the positive electrode Bp of theelectric storage device B through the common positive line Lp0. Theemitters of the upper switching elements 32 a, 32 b, and 32 c of therespective phases are connected to the collectors of the lower switchingelements 32 d, 32 e, and 32 f, respectively. The emitters of the lowerswitching elements 32 d, 32 e, and 32 f are connected to the negativeelectrode Bn of the electric storage device B through the commonnegative line Ln0. A rectifying device 33 is connected between theemitter and the collector of each of the switching elements 32 inparallel therewith. A diode is used as the rectifying device 33. A firstcontrol unit 51 of an inverter control device 5 (to be described later)individually controls switching of the gate of each of the switchingelement 32.

The switching element units 31 are connected to the rotary electricmachine MG through first wiring members Lw1 for the respective phases.The pair of switching elements 32 for each of the phases are connectedat a midpoint thereof (between the emitter of the upper switchingelement and the collector of the lower switching element) to the statorcoil of the corresponding phase of the rotary electric machine MGthrough corresponding one of the first wiring members Lw1 for therespective phases. A current sensor 35 for detecting a current flowingin the stator coil for each phase of the rotary electric machine MG isprovided at a predetermined place of corresponding one of the firstwiring members Lw1. In the present embodiment, a sensor using a Hallelement is used as the current sensor 35 described above. The currentsensor 35 includes an annular core surrounding the first wiring memberLw1 and the Hall element arranged in a cutout portion of the core. Acurrent passing through the first wiring member Lw1 for each of thephases generates a magnetic field corresponding to the amount of thecurrent in the core, and causes the Hall element to generate anelectromotive force corresponding to the amount of flux. As a result,the current flowing in the stator coil for each phase of the rotaryelectric machine MG can be detected on the basis of the magnitude of theelectromotive force.

As shown in FIG. 3, in the present embodiment, switching element units41 for the respective phases constituting the second inverter 40 areconnected in parallel with one another between the common positive lineLp0 and the common negative line Ln0. Specifically, the switchingelement units 41 are connected between three positive branch lines Lp4to Lp6 branching from the common positive line Lp0 and three negativebranch lines Ln4 to Ln6 branching from the common negative line Ln0. Inthe present embodiment, the switching element units 41 of the secondinverter 40 correspond to “switching element units” in the presentdisclosure. The switching element units 41 correspond to the threerespective phases (U-phase, V-phase, and W-phase) of stator coils of thepump motor PM.

Each of the switching element units 41 includes an upper switchingelement 42 provided on the positive electrode Bp side of the electricstorage device B with respect to a connection part of the switchingelement unit 41 and the pump motor PM, and also includes a lowerswitching element 42 provided on the negative electrode Bn side of theelectric storage device B with respect to the aforementioned connectionpart. In other words, the second inverter 40 includes upper switchingelements 42 a to 42 c, each connected to the common positive line Lp0,and lower switching elements 42 d to 42 f, each connected to the commonnegative line Ln0.

The collectors of the upper switching elements 42 a, 42 b, and 42 c ofthe respective phases are connected to the positive electrode Bp of theelectric storage device B through the common positive line Lp0. Theemitters of the upper switching elements 42 a, 42 b, and 42 c of therespective phases are connected to the collectors of the lower switchingelements 42 d, 42 e, and 42 f, respectively. The emitters of the lowerswitching elements 42 d, 42 e, and 42 f of the respective phases areconnected to the negative electrode Bn of the electric storage device Bthrough the common negative line Ln0. A rectifying device 43 isconnected between the emitter and the collector of each of the switchingelements 42 in parallel therewith. A second control unit 52 of theinverter control device 5 (to be described later) individually controlsswitching of the gate of each of the switching element 42.

The switching element units 41 are connected to the pump motor PMthrough second wiring members Lw2 for the respective phases. The pair ofswitching elements 42 for each of the phases are connected at a midpointthereof (between the emitter of the upper switching element and thecollector of the lower switching element) to a stator coil of thecorresponding phase of the pump motor PM through corresponding one ofthe second wiring members Lw2 for the respective phases. In the presentembodiment, each of the second wiring members Lw2 is not provided with acurrent sensor including a Hall element, unlike the first inverter 30.

As a substitute for the current sensor including the Hall element, ashunt resistor 45 is provided between the electric storage device B andeach of the switching element units 41 for corresponding one of thephases. In the present embodiment, the shunt resistor 45 is provided ineach of the three negative branch lines Ln4 to Ln6, so that a total ofthree shunt resistors 45 are provided. In the present embodiment, theshunt resistors 45 are mounted on a control board of the second inverter40. The shunt resistor 45 is provided to detect a current flowingthrough each of the switching element units 41 (here, the lowerswitching elements 42 d to 42 f) for the respective phases. A currentpassing through each of the lower switching elements 42 d to 42 fgenerates an electric potential difference between both ends of theshunt resistor 45 corresponding to the amount of the current, thus thecurrent flowing in the stator coil for each phase of the pump motor PMcan be detected based on the amount of the electric potential differenceand the known resistance value of the shunt resistor 45. Details of themethod for detecting the current using the shunt resistor 45 will bedescribed later.

In this way, in the present embodiment, the current sensor 35 using theHall element detects the current flowing in the stator coil for eachphase of the rotary electric machine MG, and the shunt resistor 45detects the current flowing in the stator coil for each phase of thepump motor PM. The current sensor 35 using the Hall element isexpensive, but can always accurately detect the current. By contrast,the shunt resistor 45 is inexpensive, but can detect the current onlyduring a limited time in a control period of the second inverter 40, aswill be described later. Specifically, the percentage of the periodduring which current detection can be performed by the current sensor 35relative to the control period of the first inverter 30 is higher thanthe percentage of the period during which current detection can beperformed by the shunt resistor 45 relative to the control period of thesecond inverter 40. In addition, the current sensor 35 using theexpensive Hall element has relatively stable temperature characteristicswhereas the inexpensive shunt resistor 45 is sensitive to ambienttemperature.

The rotary electric machine MG outputs the driving force transmitted tothe wheels W. Hence, control accuracy of the rotary electric machine MGneeds to be high. The pump motor PM, on the other hand, is used fordriving the rotor of the electric pump EP provided independent of thewheels W, so that the control accuracy of the pump motor PM need not beas high as that of the rotary electric machine MG. As a result ofcomprehensive consideration of these factors, the current sensors 35including the Hall elements are used for the current detection for therotary electric machine MG, and the shunt resistors 45 are used for thecurrent detection for the pump motor PM. This configuration can keep thecontrol accuracy of the rotary electric machine MG high, and reduce theproduct cost while compromising on control accuracy of the pump motor PMto some extent within an allowable range.

The expression “compromising on control accuracy of the pump motor PM tosome extent” is an expression made by taking into consideration acomparison with the case in which the current is detected using thecurrent sensors including the Hall elements in the same way as in thecase of the rotary electric machine MG. By employing the structure touse the second inverter 40 to control the pump motor PM for driving therotor of the electric pump EP, the state of the transmission device TMcan be controlled with relatively high accuracy compared with the caseof driving the pump motor PM, for example, at constant torque or at aconstant rotational speed. The structure of the present embodiment canreduce the product cost by using the inexpensive shunt resistors 45 todetect the current while allowing the state of the transmission deviceTM to be relatively accurately controlled by inverter control of thepump motor PM. The structure of the present embodiment can alsocomprehensively reduce the influence of the product cost reduction onthe control accuracy of the rotary electric machine MG and the pumpmotor PM. Moreover, mounting the shunt resistors 45 on the control boardof the second inverter 40 can effectively downsize the second inverter40, and thus the entire device.

In particular, in the structure in which the shunt resistors 45 embeddedin the second inverter 40 are arranged in the driving force source roomQ, the internal combustion engine E and the rotary electric machine MGas the driving force sources of the wheels W generate heat while thevehicle is running, so that a situation is likely to occur in which thetemperature of the installation environment of the shunt resistors 45rises to a high temperature. An increase in the amount of fluctuation inthe ambient temperature reduces the current detection accuracy obtainedby the shunt resistors 45, and, as a result, is likely to reduce thecontrol accuracy of the pump motor PM. Even in this case, the allowablerange of accuracy required for controlling the pump motor PM can absorbthe reduction in the control accuracy. Specifically, even in the case inwhich the shunt resistors 45 are disposed in the driving force sourceroom Q and placed under the high-temperature environment, the influenceon the control accuracy of the rotary electric machine MG and the pumpmotor PM can be reduced comprehensively.

3. Structure of Inverter Control Device

As shown in FIG. 3, the inverter control device 5 includes the firstcontrol unit 51 and the second control unit 52. The first control unit51 individually controls switching of the switching elements 32 of thefirst inverter 30 to control drive of the rotary electric machine MG.The second control unit 52 individually controls switching of theswitching elements 42 of the second inverter 40 to control drive of thepump motor PM. In the present embodiment, both the first control unit 51and the second control unit 52 control the drive of the rotary electricmachine MG and the pump motor PM, respectively, based on a currentvector control method.

As shown in FIG. 4, the first control unit 51 includes a rotationalspeed deriving unit 61, a three-phase/two-phase conversion unit 62, ad-axis current command value deriving unit 63, a q-axis current commandvalue deriving unit 64, a current control unit 65, a modulation factorderiving unit 66, a d-axis current adjustment command value derivingunit 67, a two-phase/three-phase conversion unit 68, and a controlsignal generation unit 69. The first control unit 51 receives a U-phasecurrent Iur, a V-phase current Ivr, and a W-phase current Iwr detectedby the current sensors 35 (refer to FIG. 3), a magnetic pole position θof the rotor Ro in the rotary electric machine MG, and a direct-currentvoltage Vdc that is a voltage on the direct-current side of the firstinverter 30. The first control unit 51 also receives target torque TR.

The rotational speed deriving unit 61 derives a rotational speed ω ofthe rotary electric machine MG based on the magnetic pole position θ.The derived rotational speed ω is provided to the current control unit65 and the two-phase/three-phase conversion unit 68. Thethree-phase/two-phase conversion unit 62 derives a d-axis current Idrand a q-axis current Iqr based on the U-phase current Iur, the V-phasecurrent Ivr, and the W-phase current Iwr, and the magnetic pole positionθ. The derived d-axis and q-axis currents Idr and Iqr are provided tothe current control unit 65.

The d-axis current command value deriving unit 63 derives a basic d-axiscurrent command value Idb based on the target torque TR. The basicd-axis current command value Idb corresponds to a command value for ad-axis current when maximum torque control is performed. The maximumtorque control is a control to adjust a current phase so as to maximizeoutput torque of the rotary electric machine MG for the same current. Inthe present embodiment, the d-axis current command value deriving unit63 uses a predetermined map to derive the basic d-axis current commandvalue Idb corresponding to the value of the target torque TR. A d-axiscurrent adjustment command value ΔId is derived by the d-axis currentadjustment command value deriving unit 67 (to be described later) andsubtracted from the basic d-axis current command value Idb to obtain ad-axis current command value Id, which is provided to the currentcontrol unit 65.

The q-axis current command value deriving unit 64 derives a q-axiscurrent command value Iq based on the target torque TR. In the presentembodiment, the q-axis current command value deriving unit 64 uses apredetermined map to derive the q-axis current command value Iqcorresponding to the value of the target torque TR. If the d-axiscurrent adjustment command value deriving unit 67 (to be describedlater) has derived the d-axis current adjustment command value ΔId, theq-axis current command value deriving unit 64 derives the q-axis currentcommand value Iq in accordance with the values of the target torque TRand the d-axis current adjustment command value ΔId. The derived q-axiscurrent command value Iq is provided to the current control unit 65.

The current control unit 65 determines a d-axis voltage command value Vdand a q-axis voltage command value Vq based on the d-axis currentcommand values Id and the q-axis current command value Iq, the d-axiscurrent Idr and the q-axis current Iqr, and the rotational speed ω. Thecurrent control unit 65 performs current feedback control with respectto the d-axis current command value Id and the q-axis current commandvalue Iq to determine the d-axis voltage command value Vd and the q-axisvoltage command value Vq. The determined d-axis and q-axis voltagecommand values Vd and Vq are provided to the modulation factor derivingunit 66 and the two-phase/three-phase conversion unit 68.

The modulation factor deriving unit 66 derives a modulation factor Mfbased on the d-axis voltage command value Vd and the q-axis voltagecommand value Vq, and the direct-current voltage Vdc. The modulationfactor deriving unit 66 derives the modulation factor Mf by Expression(1) below.

Mf=√(Vd ² +Vq ²)/Vdc  (1)

The modulation factor Mf serves as an indicator representing a ratio ofthe effective value of the fundamental wave component in an outputvoltage waveform from the first inverter 30 to the direct-currentvoltage Vdc. The derived modulation factor Mf is provided to the d-axiscurrent adjustment command value deriving unit 67.

The d-axis current adjustment command value deriving unit 67 derives thed-axis current adjustment command value ΔId based on the modulationfactor Mf and a predetermined reference modulation factor (for example,0.78). If the modulation factor Mf exceeds the reference modulationfactor, the d-axis current adjustment command value deriving unit 67derives the d-axis current adjustment command value ΔId (ΔId>0) based onthe deviation of the modulation factor Mf from the reference modulationfactor.

The d-axis current adjustment command value ΔId is a command value forgiving a field-weakening current, which works to weaken the magneticfield flux of the rotor Ro in the rotary electric machine MG.Specifically, after the d-axis current adjustment command value ΔId isderived, field-weakening control is performed to adjust phases ofalternating-current voltage commands so that the magnetic field producedby the stator coil of the rotary electric machine MG changes so as toweaken the magnetic field flux of the rotor Ro. The d-axis currentadjustment command value ΔId is provided to the q-axis current commandvalue deriving unit 64. The d-axis current adjustment command value ΔIdis subtracted from the basic d-axis current command value Idb derived bythe d-axis current command value deriving unit 63 to obtain the d-axiscurrent command value Id, which in turn is provided to the currentcontrol unit 65.

The two-phase/three-phase conversion unit 68 derives a U-phase voltagecommand value Vu, a V-phase voltage command value Vv, and a W-phasevoltage command value Vw as the alternating-current voltage commandsbased on the d-axis voltage command value Vd and the q-axis voltagecommand value Vq, and the magnetic pole position θ. The derivedthree-phase alternating-current voltage command values Vu, Vv, and Vware provided to the control signal generation unit 69.

The control signal generation unit 69 generates control signals(switching control signals) S11 to S16 for individually controlling theswitching of the switching elements 32 a to 32 f of the first inverter30 based on the U-phase voltage command value Vu, the V-phase voltagecommand value Vv, and the W-phase voltage command value Vw. The controlsignal generation unit 69 generates the control signals S11 to S16 forat least pulse-width modulation (PWM) control. The control signalgeneration unit 69 generates the control signals S11 to S16 for the PWMcontrol based on a comparison in magnitude between the carrier (carrierwave) and the alternating-current voltage command values Vu, Vv, and Vw.The carrier is formed, for example, of a triangular wave or a sawtoothwave. The control signal generation unit 69 may be structured togenerate the control signals S11 to S16 for known overmodulation PWMcontrol or rectangular wave control, depending on, for example, themagnitude of the modulation factor Mf.

The second control unit 52 has basically the same structure as that ofthe first control unit 51 although the pump motor PM serves as acontrolled object of the second control unit 52 whereas the rotaryelectric machine MG serves as a controlled object of the first controlunit 51. However, the d-axis current adjustment command value derivingunit 67 in the second control unit 52 derives the d-axis currentadjustment command value ΔId under a “specified condition” even if themodulation factor Mf is not larger than the reference modulation factor.In this way, the second control unit 52 is structured to perform thefield-weakening control even when the “specified condition” issatisfied, regardless of the magnitude of the modulation factor Mf. Thisfeature will be described later. The control signal generation unit 69in the second control unit 52 is structured to generate control signalsS21 to S26 dedicated for the PWM control. The other features are thesame as those of the first control unit 51, so that the details thereofwill not be described here.

4. Method for Detecting Current Using Shunt Resistors

As described above, the second control unit 52 generates the controlsignals S21 to S26 for the PWM control, and individually controls theswitching elements 42 based on the control signals S21 to S26 to controlthe pump motor PM by the PWM control. In the present embodiment, the PWMcontrol means a continuous pulse-width modulation (CPWM), such as asinusoidal PWM or a space vector PWM. As is well known, the PWM controlmodulates the alternating-current voltage command values Vu, Vv, and Vwinto discrete pulse signals. FIG. 5 schematically shows enlargedwaveforms of the control signals S21 to S26 together with the carrier,in a predetermined period.

As shown in FIG. 5, the control signal S21 is at a high (H) level whenthe U-phase voltage command value Vu is not lower than the carrier, andis at a low (L) level when the U-phase voltage command value Vu is lowerthan the carrier. The upper switching element 42 a for the U-phase is ONwhen the control signal S21 is at the high (H) level, and is OFF whenthe control signal S21 is at the low (L) level. The control signals S22and S23 are also generated based on the comparison of the voltagecommand values Vv and Vw with the carrier, and the upper switchingelement 42 b for the V-phase and the upper switching element 42 c forthe W-phase are also switched between ON and OFF in the same way.

The levels of the control signals S24 to S26 at each time are oppositeto the levels of the control signals S21 to S23, respectively. Thecontrol signal S24 is at the low (L) level while the control signal S21is at the high (H) level, and the control signal S24 is at the high (H)level while the control signal S21 is at the low (L) level. The sameapplies to the relation between the control signal S22 and the controlsignal S25, and the relation between the control signal S23 and thecontrol signal S26. As a result, the upper switching elements 42 a to 42c for the respective phases and the lower switching elements 42 d to 42f, respectively, for the corresponding phases are switched in acomplementary manner. In practice, a dead time exists in which two upperand lower switching elements 42 included in each of the switchingelement units 41 are both OFF. The dead time is, however, omitted fromthe description for simplicity.

Attention to mutual relations among the three-phase control signals S21to S23 (or control signals S24 to S26) reveals that a period is presentin which the three-phase control signals are at mixed levels of the high(H) and the low (L) levels, and another period is present in which thethree-phase control signals are at the same level. In this description,the former is called an “active vector period”, and the latter is calleda “zero vector period”. FIG. 5 shows the zero vector period withhatching.

As an example of the active vector period, at a time, for example,indicated as (A) in FIG. 5, the upper switching element 42 a for theU-phase is ON, and the upper switching elements 42 b and 42 c for theV-phase and the W-phase are OFF. At this time, the electric storagedevice B (capacitor C) is conducted to the pump motor PM via the secondinverter 40, and the current flows therethrough (refer to FIG. 6).Specifically, the current flows through a path from the positiveelectrode Bp side of the electric storage device B (capacitor C), via,sequentially, the upper switching element 42 a for the U-phase, the pumpmotor PM, and the lower switching elements 42 e and 42 f for the V-phaseand the W-phase, then to the negative electrode Bn side of the electricstorage device B (capacitor C).

In this case, the currents of the V-phase and the W-phase flow in two ofthe shunt resistors 45 provided in the negative branch lines Ln5 andLn6, so that the currents flowing in the stator coils of the V-phase andthe W-phase can be detected. The current of the U-phase flows in thepositive branch line Lp4, and does not flow in the shunt resistor 45provided in the negative branch line Ln4. Therefore, the current flowingin the stator coil of the U-phase cannot be detected. Also, in otheractive vector periods, the current or currents flowing in the statorcoil or stator coils of one phase or two phases can be detected in thesame way in accordance with the pattern of the path conducting thecurrent or currents.

The zero vector period includes a period in which all the upperswitching elements 42 a to 42 c for the three phases are ON and a periodin which all the upper switching elements 42 a to 42 c are OFF. In otherwords, the zero vector period includes a period in which all the lowerswitching elements 42 d to 42 f for the three phases are OFF and aperiod in which all the lower switching elements 42 d to 42 f are ON. Inthis description, the former is called a “lower full-off period Tf”, andthe latter is called a “lower full-on period Tn”. The lower full-offperiod Tf is a period in which all the switching elements 42 on the sideprovided with the shunt resistors 45 are OFF, and can also be called a“target full-off period”. In the same sense, the lower full-on period Tncan be called a “target full-on period”. No current flows between theelectric storage device B and the pump motor PM during the zero vectorperiod. During the zero vector period, however, currents circulatebetween the second inverter 40 and the pump motor PM. The circulationpattern of the currents differs between the lower full-on period Tn andthe lower full-off period Tf.

At a time during the lower full-on period Tn indicated, for example, as(B) in FIG. 5, all the lower switching elements 42 d to 42 f for thethree phases are ON. At this time, the currents circulate through thelower switching elements 42 d to 42 f (or the corresponding rectifyingdevices 43) for the three phases (refer to FIG. 7). Specifically, thecurrents circulate in a closed circuit from the pump motor PM, via,sequentially, the lower switching elements 42 e and 42 f for the V-phaseand the W-phase and the rectifying device 43 connected in parallel withthe lower switching element 42 d for the U-phase, then back to the pumpmotor PM.

In this case, the currents flow through all the three shunt resistors 45provided in the negative branch lines Ln4 to Ln6. The inverter controldevice 5 (second control unit 52) utilizes this phenomenon to performthe current detection process using the shunt resistors 45 during thelower full-on period Tn. In other words, the inverter control device 5simultaneously detects the currents flowing in the stator coils of therespective phases of the pump motor PM during the lower full-on periodTn. As described above, each of the currents flowing in the stator coilsof the respective phases of the pump motor PM is detected based on theelectric potential difference between both ends of the correspondingshunt resistor 45.

At a time during the lower full-off period Tf indicated, for example, as(C) in FIG. 5, all the lower switching elements 42 d to 42 f for thethree phases are OFF (all the upper switching elements 42 a to 42 c forthe three phases are ON). At this time, the currents circulate throughthe upper switching elements 42 a to 42 c (or the correspondingrectifying devices 43) for the three phases (refer to FIG. 8).Specifically, the currents circulate in a closed circuit from the pumpmotor PM, via, sequentially, the rectifying devices 43 respectivelyconnected in parallel with the upper switching elements 42 b and 42 cfor the V-phase and the W-phase and the upper switching element 42 a forthe U-phase, then back to the pump motor PM.

In this case, theoretically, no current flows in any of the three shuntresistors 45 provided in the negative branch lines Ln4 to Ln6. Inpractice, however, the three shunt resistors 45 detect small currentsduring the lower full-off period Tf. These small currents cause an errorin the zero point (origin) in the current detection process performedduring the lower full-on period Tn. To solve this problem, the invertercontrol device 5 uses the shunt resistors 45 to detect the smallcurrents flowing in the stator coils of the respective phases of thepump motor PM during the lower full-off period Tf. In other words, theinverter control device 5 simultaneously detects the small currentsflowing in the stator coils of the respective phases of the pump motorPM during the lower full-off period Tf. The inverter control device 5uses the small currents of the respective phases detected during thelower full-off period Tf in this way to calculate an offset correctionamount ΔOc at the zero point in the current detection process describedabove.

A study conducted by the inventors of the present disclosure has foundthat the amounts of the currents detected by the shunt resistors 45during the lower full-off period Tf are not uniform, but the amounts ofthe currents flowing in the stator coils of the respective phases of thepump motor PM are correlated with one another. In view of this point, inthe present embodiment, the inverter control device 5 divides anelectrical angle period Tc of the pump motor PM into a plurality ofdivided periods Td, and individually determines the offset correctionamount ΔOc for each of the divided periods Td. More specifically, theinverter control device 5 stores (accumulates) the individual offsetcorrection amount previously determined for each of the divided periodsTd. Then, based on the accumulated offset correction amounts, theinverter control device 5 determines the offset correction amount ΔOc asa value obtained by statistically processing (for example, bycalculating the average value, a weighted average value, the mode value,or the median value, over a specified time period, of) the accumulatedoffset correction amounts. The offset correction amount ΔOc for each ofthe divided periods Td is determined for each of the shunt resistors 45.The number of the divided periods Td may be set to an appropriate value,but is preferably set to 2^(K) (K represents a natural number of 10 orless).

The inverter control device 5 uses the offset correction amount ΔOcdetermined as described above to detect an actual current flowing ineach of the stator coils of the respective phases of the pump motor PM.The inverter control device 5 detects, for each phase, the actualcurrent (“Ir” shown in FIG. 9) flowing in the stator coil, by using theoffset correction amount ΔOc to correct a current detection value(“Idet” shown in FIG. 9) obtained by the current detection processexecuted during the lower full-on period Tn. Specifically, the invertercontrol device 5 detects, for each phase, the actual current (Ir)flowing in the stator coil by subtracting the offset correction amountΔOc assigned to one of the divided periods Td corresponding thereto fromthe actually obtained current detection value (Idet). The detectedactual current values of the respective phases are provided, as theU-phase current Iur, the V-phase current Ivr, and the W-phase currentIwr (refer to FIG. 4), for the current feedback control performed by thesecond control unit 52.

As described above, in the present embodiment, the shunt resistors 45embedded in the second inverter 40 are disposed in the driving forcesource room Q, so that the periphery of the shunt resistors 45 is likelyto be heated to a high temperature, and the amount of fluctuation in thetemperature is likely to increase. The increase in the amount offluctuation in the ambient temperature reduces the current detectionaccuracy obtained by the shunt resistors 45, and, as a result, is likelyto reduce the control accuracy of the pump motor PM. A technique isknown in which the offset at the zero point is corrected when the devicestarts up. However, the technique alone is not sufficient to deal withthe large fluctuation in the ambient temperature, which is a problem. Inthis respect, in the present embodiment, the offset correction amountΔOc is determined during the lower full-off period Tf repeatedlyappearing during the drive control of the pump motor PM, so that theoffset can be repeatedly corrected, and hence, the fluctuation in theambient temperature can be dealt with. As a result, the detectionaccuracy in the current detection process can be increased.

In the present embodiment, the electric potential difference is actuallysampled at the middle (intermediate time) of the lower full-on period Tnin the current detection process. The electric potential differencebetween both ends of each of the shunt resistors 45 is very small, sothat an operational amplifier (not shown) amplifies output signals fromthe shunt resistors 45 during the sampling. In other words, the secondcontrol unit 52 includes the amplifying circuit for amplifying theoutput signals from the shunt resistors 45. However, a general-purposeoperational amplifier has a slew rate that is set to a relatively smallvalue, and hence, the maximum response speed thereof is limited.Specifically, the temporal change rate of the output values from theshunt resistors 45 has an upper limit given by the slew rate (changerate limit value) set in advance for the operational amplifier.

FIG. 10 schematically shows examples of modes of change in one of theoutput signals from the shunt resistors 45 obtained through theoperational amplifier during the lower full-on period Tn. As can beunderstood from the upper diagram of FIG. 10, in a situation of, forexample, increasing the output torque of the pump motor PM, if the lowerfull-on period Tn is fairly short, the electric potential differencesampling may be performed while the output signal from the shuntresistor 45 has not been fully amplified. In such a case, the currentflowing in each of the stator coils of the respective phases of the pumpmotor PM is falsely detected (detected as a value different from anactual value), so that the control accuracy of the pump motor PM isreduced. For example, if a value smaller than the actual current isprovided for the current feedback control as the current detectionvalue, a larger force acts to eliminate a current deviation calculatedto be larger than an actual value. As a result, the current flowing inthe stator coil may increase to an unnecessarily large value.

To solve this problem, in the present embodiment, if the lower full-onperiod Tn is shorter than a predetermined reference time Tr, theinverter control device 5 performs an adjusting process to adjustparameters for the current feedback control of the pump motor PM so asto increase the lower full-on period Tn. The reference time Tr is setbased on the change rate limit value (slew rate) set in advance for theoperational amplifier as the upper limit value of the temporal changerate of the output values from the shunt resistors 45. The referencetime Tr is preferably set, based on an expected maximum value of theoutput values from the shunt resistors 45, to a time twice or more atime obtained by dividing the maximum value by the change rate limitvalue. Examples of the parameters to be adjusted include, but are notlimited to, the carrier frequency in the PWM control and the modulationfactor Mf in the current vector control. These parameters may beadjusted in an alternative manner or in a combined manner.

The present embodiment is structured such that the carrier frequency inthe PWM control is continuously changeable. As an embodiment of theadjusting process, if the lower full-on period Tn is shorter than thereference time Tr, the inverter control device 5 reduces the carrierfrequency in the PWM control (refer to the lower diagram of FIG. 10).The control signals S21 to S26 are generated based on a comparison inmagnitude between the carrier and the alternating-current voltagecommand values Vu, Vv, and Vw. Hence, reducing the carrier frequency(increasing the carrier period) increases the duration time of the ONstate of each of the lower switching elements 42 d to 42 f for therespective phases. Moreover, the duration time of the ON state of eachof the lower switching elements 42 d to 42 f for the respective phasescan be increased while keeping a duty ratio constant. As a result, thelower full-on period Tn can be increased.

In the present embodiment, the inverter control device 5 reduces thecarrier frequency to a frequency at which the lower full-on period Tn isequal to the reference time Tr. This configuration can ensure thereference time Tr as the lower full-on period Tn, and hence, canrestrain the sampling of the output signal from the shunt resistor 45that has not been fully amplified due to the slew rate of theoperational amplifier. As a result, correctness of the current detectionprocess can be ensured. In that case, the amount of reduction in thecarrier frequency can be minimized to a necessary level. As a result,for example, degradation in controllability and generation of noise ofthe pump motor PM can be effectively reduced.

As another embodiment of the adjusting process, if the lower full-onperiod Tn is shorter than the reference time Tr, the inverter controldevice 5 reduces the modulation factor Mf in the current vector control.The inverter control device 5 performs the field-weakening control toreduce the modulation factor Mf. In the present embodiment, thephenomenon that “the lower full-on period Tn is shorter than thereference time Tr” corresponds to the “specified condition” mentionedabove as one of the conditions to start the field-weakening control.After the field-weakening control is performed and the d-axis currentadjustment command value ΔId is derived, d-axis current command value Iddecreases (changes in the negative direction), as clearly seen from FIG.4. In general, the q-axis current command value Iq derived based on thepredetermined map also decreases along a constant torque line, as shownin FIG. 11. As a result, the current deviation in the current feedbackcontrol decreases, and the voltage command values Vd and Vq derived bythe current control unit 65 also decreases. Consequently, the executionof the field-weakening control reduces the modulation factor Mf, asclearly understood from Expression (1) given above.

The modulation factor Mf is an indicator representing a ratio of theeffective value of the fundamental wave component in an output voltagewaveform from the second inverter 40 to the direct-current voltage Vdc,and therefore, reducing the modulation factor Mf reduces the duty ratio.Reducing the duty ratio reduces the duration time of the ON state ofeach of the upper switching elements 42 a to 42 c for the respectivephases, and increases the duration time of the ON state of each of thelower switching elements 42 d to 42 f for the respective phases by anamount corresponding to the reduction in the duration time. As a result,the lower full-on period Tn can be increased.

The inverter control device 5 reduces the modulation factor Mf so thatthe lower full-on period Tn is not shorter than the reference time Tr.To achieve this, for example, it is recommended to experimentallydetermine in advance a second reference modulation factor that increasesthe lower full-on period Tn to be not shorter than the reference timeTr. The d-axis current adjustment command value deriving unit 67 ispreferably structured to derive the d-axis current adjustment commandvalue ΔId based on the second reference modulation factor (for example,a value roughly in the range from 0.6 to 0.7) obtained as an empiricalvalue and the modulation factor Mf. This structure can also ensure thereference time Tr as the lower full-on period Tn, and hence, canrestrain the sampling of the output signal from the shunt resistor 45that has not been fully amplified due to the slew rate of theoperational amplifier. As a result, correctness of the current detectionprocess can be ensured. In that case, the output torque of the pumpmotor PM can be kept constant.

5. Other Embodiments

Finally, other embodiments of the drive device according to the presentdisclosure will be described. Any structure disclosed in each of thefollowing embodiments can be applied in combination with structuresdisclosed in other embodiments unless any contradiction occurs.

(1) The embodiment above has been described by exemplifying thestructure (three-shunt structure) in which the shunt resistor 45 isprovided in each of the three negative branch lines Ln4 to Ln6. Theembodiments of the present disclosure are, however, not limited to thisstructure. For example, the structure may be a structure (two-shuntstructure) in which the shunt resistor 45 is provided in each of any twoof the three negative branch lines Ln4 to Ln6. The sum of instantaneousvalues of currents of the respective phases is zero, so that thisstructure also allows appropriate detection of the currents flowing inthe stator coils of the respective phases of the pump motor PM.Alternatively, the structure may be a structure (one-shunt structure) inwhich one shunt resistor 45 is provided in the common negative line Ln0.

(2) The embodiment above has been described by exemplifying thestructure in which the shunt resistors 45 are provided in the negativebranch lines Ln4 to Ln6 so as to detect the currents flowing in therespective lower switching elements 42 d to 42 f for the correspondingphases. The embodiments of the present disclosure are, however, notlimited to this structure. For example, the shunt resistors 45 may beprovided in the positive branch lines Lp4 to Lp6 or in the commonpositive line Lp0 so as to detect the currents flowing in the respectiveupper switching elements 42 a to 42 c for the corresponding phases.However, this case requires installation of another circuit forgenerating a reference electric potential.

(3) The embodiment above has been described by way of the example inwhich the sensor including the core and the Hall element is used as thecurrent sensor 35 for detecting the current flowing in the stator coilfor each phase of the rotary electric machine MG. The embodiments of thepresent disclosure are, however, not limited to this structure. Anyother sensor may be used provided that the percentage of the periodduring which current detection can be performed by the sensor relativeto the control period of the first inverter 30 is higher than thepercentage of the period during which current detection can be performedby the shunt resistor 45 relative to the control period of the secondinverter 40. For example, a coreless current sensor using a Hallelement, a current sensor using a magnetic coil, or a current sensorusing a coreless coil may be used.

(4) The embodiment above has been described by exemplifying thestructure in which the second inverter 40 controls the pump motor PMdrivingly connected to the rotor of the oil discharging electric pump EPprovided independent of the wheels W. The embodiments of the presentdisclosure are, however, not limited to this structure. For example, thesecond inverter 40 may be structured to control an alternating-currentrotary electric machine drivingly connected to a rotating body otherthan the rotor of the electric pump EP. Examples of such a rotating bodyinclude, but are not limited to, rotors of a drive motor for coolingwater discharge, a drive motor for an air conditioner compressor, adrive motor for an electric power steering, and a drive motor for acooling fan.

(5) The embodiment above has been described by exemplifying theinverter-caseless structure in which the first inverter 30 and thesecond inverter 40 are integrally fixed to the case 2. The embodimentsof the present disclosure are, however, not limited to this structure.For example, the first inverter 30 and the second inverter 40 may beaccommodated in the dedicated inverter case separate from the case 2,and the dedicated inverter case and the case 2 may be disposed in thedriving force source room Q.

(6) The embodiment above has been described by exemplifying thestructure in which the inverter control device 5 individually determinesthe offset correction amount ΔOc in each of the divided periods Tddefined by dividing the electrical angle period Tc of the pump motor PM.The embodiments of the present disclosure are, however, not limited tothis structure. For example, the inverter control device 5 may determinea uniform value of the offset correction amount ΔOc for the entireelectrical angle period Tc of the pump motor PM, without setting thedivided periods Td.

(7) The embodiment above has been described by exemplifying thestructure in which the carrier frequency in the PWM control iscontinuously changeable. The embodiment above has also been described byexemplifying the structure in which, if the lower full-on period Tn isshorter than the reference time Tr, the inverter control device 5reduces the carrier frequency to a frequency at which the lower full-onperiod Tn is equal to the reference time Tr. The embodiments of thepresent disclosure are, however, not limited to these structures. Forexample, an embodiment may be structured such that the carrier frequencyin the PWM control is changeable in a step-like manner. In this case, ifthe lower full-on period Tn is shorter than the reference time Tr, theinverter control device 5 preferably reduces the carrier frequency tothe highest frequency in a range of the carrier frequency changeable ina step-like manner at which the lower full-on period Tn is not shorterthan the reference time Tr. In either of the structures in which thecarrier frequency is changeable in a continuous manner or a step-likemanner, the inverter control device 5 may reduce the carrier frequencyto any frequency at which the lower full-on period Tn is not shorterthan the reference time Tr.

(8) The embodiment above has been described by exemplifying thestructure in which, if the lower full-on period Tn is shorter than thereference time Tr, the inverter control device 5 performs thefield-weakening control to reduce the modulation factor Mf. Theembodiments of the present disclosure are, however, not limited to thisstructure. For example, in a structure in which a voltage boostingcircuit is provided between the electric storage device B and thecapacitor C, the inverter control device 5 may control the voltageboosting circuit to raise the direct-current voltage Vdc so as to reducethe modulation factor Mf.

(9) It should be understood that the other structures of the embodimentsdisclosed herein are also merely examples in all respects, and the scopeof the present disclosure is not limited by those embodiments. Thoseskilled in the art will easily understand that appropriate modificationscan be made without departing from the gist of the present disclosure.Accordingly, the scope of the present disclosure naturally includes alsoother embodiments that are modified without departing from the gist ofthe present disclosure.

(10) Moreover, in addition to the drive device according to the presentdisclosure, the inverter control device having the function ofaccurately detecting the currents flowing in the stator coils of therespective phases of the alternating-current rotary electric machineusing the shunt resistors has the following major characteristicfeatures.

The inverter control device 5 controlling drive of the inverter that isconnected to the electric storage device B serving as the direct-currentpower supply and to the alternating-current rotary electric machinedriven by an N-phase alternating current (N is a natural number of 2 ormore) and that performs direct-current/alternating-current conversionhas a first characteristic feature of:

including N or (N−1) shunt resistors 45 detecting the currents flowingin the alternating-current rotary electric machine between the electricpole line Lp or Ln of the electric storage device B and the switchingelements for the respective phases included in the inverter;

controlling the alternating-current rotary electric machine by PWMcontrol by individually controlling the switching of the upper switchingelements and the lower switching elements; and

performing the current detection process of detecting the currentsflowing in the stator coils of the respective phases of thealternating-current rotary electric machine during the target full-onperiod in which the switching elements on the installation side providedwith the shunt resistors 45 for the respective phases are all ON.

In such a structure, the inverter control device 5 has a secondcharacteristic feature of performing any one or a combination of morethan one of the following items (a) to (c).

(a) Determining the offset correction amount ΔOc at the zero point inthe current detection process during the target full-off period in whichthe switching elements for the respective phases provided on theinstallation side are all OFF.

(b) Reducing the carrier frequency in the PWM control if the targetfull-on period is shorter than the predetermined reference time Tr.

(c) Reducing the modulation factor Mf representing the ratio of theeffective value of the alternating-current voltage commands Vu, Vv, andVw to the direct-current voltage Vdc of the inverter if the targetfull-on period is shorter than the predetermined reference time Tr.

The inverter control device having these characteristic structures canalso provide the various operational advantages related to the drivedevice described in the embodiments above. In this case, the severaladditional techniques illustrated as the examples of preferablestructures for the drive device described in the embodiments above canbe incorporated in the inverter control device. If the severaladditional techniques are incorporated, the operational advantagescorresponding thereto can be obtained. The inverter control device asdescribed above can naturally be used not only in the drive device for avehicle, but also in various devices (such as electrical appliances andlarge industrial equipment) each including an inverter for controllingan alternating-current rotary electric machine driven by a multi-phasealternating current.

INDUSTRIAL APPLICABILITY

The present disclosure can be used, for example, for a drive device fora hybrid vehicle.

1. A drive device comprising: an alternating-current rotary electricmachine in which currents of a plurality of phases flow; an inverterthat includes switching element units for respective phasescorresponding to the respective phases, and that is connected between adirect-current power supply and the alternating-current rotary electricmachine and performs conversion between a direct current and analternating current; and shunt resistors that detect currents flowing inthe respective switching element units for the corresponding phasesbetween the direct-current power supply and the switching element unitsfor the respective phases, wherein the alternating-current rotaryelectric machine is drivingly connected to a rotating body providedindependent of wheels, and the shunt resistors are disposed in a drivingforce source room accommodating a driving force source of the wheels. 2.The drive device according to claim 1, further comprising a drivetransmission device that operates with hydraulic pressure suppliedthereto and controls a transmission state of driving force from thedriving force source to the wheels, wherein the rotating body is a rotorof an electric pump that discharges oil supplied to the drivetransmission device.
 3. The drive device according to claim 1, whereinthe alternating-current rotary electric machine is structured such thatN-phase currents (N is a natural number of 2 or more) flow therein, apositive electrode of the direct-current power supply is connected tothe switching element units for the respective phases through a commonpositive line common to the N switching element units for the respectivephases and N positive branch lines branching from the common positiveline and connected to the respective switching element units for therespective phases, and a negative electrode of the direct-current powersupply is connected to the switching element units for the respectivephases through a common negative line common to the N switching elementunits for the respective phases and N negative branch lines branchingfrom the common negative line and connected to the respective switchingelement units for the respective phases, and the shunt resistors areprovided in respective N or (N−1) negative branch lines.
 4. The drivedevice according to claim 1, further comprising an inverter controldevice that controls drive of the inverter, wherein each of theswitching element units for the respective phases includes an upperswitching element and a lower switching element, the upper switchingelement being provided closer to the positive electrode of thedirect-current power supply than a connection part of the switchingelement unit to the alternating-current rotary electric machine, thelower switching element being provided closer to the negative electrodeof the direct-current power supply than the connection part, each of theshunt resistors is provided so as to detect a current flowing in thelower switching element of corresponding one of the switching elementunits for the respective phases, and the inverter control devicecontrols the alternating-current rotary electric machine by PWM controlby individually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases, performs a current detection process of detectingthe currents of the respective phases flowing in the alternating-currentrotary electric machine based on an electric potential differencebetween both ends of each of the shunt resistors during a lower full-onperiod in which the lower switching elements of the switching elementunits for the respective phases are all ON, and determines an offsetcorrection amount at a zero point in the current detection process basedon the electric potential difference between both ends of each of theshunt resistors during a lower full-off period in which the lowerswitching elements of the switching element units for the respectivephases are all OFF.
 5. The drive device according to claim 4, whereinthe inverter control device individually determines the offsetcorrection amount for each of the shunt resistors in each of a pluralityof divided periods defined by dividing an electrical angle period of thealternating-current rotary electric machine.
 6. The drive deviceaccording to claim 1, further comprising an inverter control device thatcontrols drive of the inverter, wherein each of the switching elementunits for the respective phases includes an upper switching element anda lower switching element, the upper switching element being provided onthe positive electrode side of the direct-current power supply withrespect to a connection part of the switching element unit and thealternating-current rotary electric machine, the lower switching elementbeing provided on the negative electrode side of the direct-currentpower supply with respect to the connection part, each of the shuntresistors is provided so as to detect a current flowing in the lowerswitching element of corresponding one of the switching element unitsfor the respective phases, and the inverter control device controls thealternating-current rotary electric machine by PWM control byindividually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases, performs a current detection process of detectingthe currents of the respective phases flowing in the alternating-currentrotary electric machine based on an electric potential differencebetween both ends of each of the shunt resistors during a lower full-onperiod in which the lower switching elements of the switching elementunits for the respective phases are all ON, and reduces a carrierfrequency in the PWM control when the lower full-on period is shorterthan a predetermined reference time.
 7. The drive device according toclaim 6, wherein the inverter control device is structured such that thecarrier frequency can be changed in a continuous manner or a step-likemanner, and when the lower full-on period is shorter than the referencetime, reduces the carrier frequency to a highest frequency in a range ofthe changeable carrier frequency at which the lower full-on period isnot shorter than the reference time.
 8. The drive device according toclaim 1, further comprising an inverter control device that controlsdrive of the inverter, wherein each of the switching element units forthe respective phases includes an upper switching element and a lowerswitching element, the upper switching element being provided on thepositive electrode side of the direct-current power supply with respectto a connection part of the switching element unit and thealternating-current rotary electric machine, the lower switching elementbeing provided on the negative electrode side of the direct-currentpower supply with respect to the connection part, each of the shuntresistors is provided so as to detect a current flowing in the lowerswitching element of corresponding one of the switching element unitsfor the respective phases, and the inverter control device controls thealternating-current rotary electric machine by PWM control byindividually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases based on alternating-current voltage commands thatare commands for alternating-current voltages of a plurality of phases,performs a current detection process of detecting the currents of therespective phases flowing in the alternating-current rotary electricmachine based on an electric potential difference between both ends ofeach of the shunt resistors during a lower full-on period in which thelower switching elements of the switching element units for therespective phases are all ON, and reduces a modulation factorrepresenting a ratio of an effective value of the alternating-currentvoltage commands to a voltage on the direct-current side of the inverterwhen the lower full-on period is shorter than a predetermined referencetime.
 9. The drive device according to claim 8, wherein the invertercontrol device is structured to control the alternating-current rotaryelectric machine by current vector control, and reduces the modulationfactor by performing field-weakening control to adjust thealternating-current voltage commands so as to change a magnetic fieldgenerated by stator coils of the alternating-current rotary electricmachine to have a direction of weakening a magnetic field flux of arotor.
 10. The drive device according to claim 2, wherein thealternating-current rotary electric machine is structured such thatN-phase currents (N is a natural number of 2 or more) flow therein, apositive electrode of the direct-current power supply is connected tothe switching element units for the respective phases through a commonpositive line common to the N switching element units for the respectivephases and N positive branch lines branching from the common positiveline and connected to the respective switching element units for therespective phases, and a negative electrode of the direct-current powersupply is connected to the switching element units for the respectivephases through a common negative line common to the N switching elementunits for the respective phases and N negative branch lines branchingfrom the common negative line and connected to the respective switchingelement units for the respective phases, and the shunt resistors areprovided in respective N or (N−1) negative branch lines.
 11. The drivedevice according to claim 2, further comprising an inverter controldevice that controls drive of the inverter, wherein each of theswitching element units for the respective phases includes an upperswitching element and a lower switching element, the upper switchingelement being provided closer to the positive electrode of thedirect-current power supply than a connection part of the switchingelement unit to the alternating-current rotary electric machine, thelower switching element being provided closer to the negative electrodeof the direct-current power supply than the connection part, each of theshunt resistors is provided so as to detect a current flowing in thelower switching element of corresponding one of the switching elementunits for the respective phases, and the inverter control devicecontrols the alternating-current rotary electric machine by PWM controlby individually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases, performs a current detection process of detectingthe currents of respective phases flowing in the alternating-currentrotary electric machine based on an electric potential differencebetween both ends of each of the shunt resistors during a lower full-onperiod in which the lower switching elements of the switching elementunits for the respective phases are all ON, and determines an offsetcorrection amount at a zero point in the current detection process basedon the electric potential difference between both ends of each of theshunt resistors during a lower full-off period in which the lowerswitching elements of the switching element units for the respectivephases are all OFF.
 12. The drive device according to claim 2, furthercomprising an inverter control device that controls drive of theinverter, wherein each of the switching element units for the respectivephases includes an upper switching element and a lower switchingelement, the upper switching element being provided on the positiveelectrode side of the direct-current power supply with respect to aconnection part of the switching element unit and thealternating-current rotary electric machine, the lower switching elementbeing provided on the negative electrode side of the direct-currentpower supply with respect to the connection part, each of the shuntresistors is provided so as to detect a current flowing in the lowerswitching element of corresponding one of the switching element unitsfor the respective phases, and the inverter control device controls thealternating-current rotary electric machine by PWM control byindividually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases, performs a current detection process of detectingthe currents of the respective phases flowing in the alternating-currentrotary electric machine based on an electric potential differencebetween both ends of each of the shunt resistors during a lower full-onperiod in which the lower switching elements of the switching elementunits for the respective phases are all ON, and reduces a carrierfrequency in the PWM control when the lower full-on period is shorterthan a predetermined reference time.
 13. The drive device according toof claim 2, further comprising an inverter control device that controlsdrive of the inverter, wherein each of the switching element units forthe respective phases includes an upper switching element and a lowerswitching element, the upper switching element being provided on thepositive electrode side of the direct-current power supply with respectto a connection part of the switching element unit and thealternating-current rotary electric machine, the lower switching elementbeing provided on the negative electrode side of the direct-currentpower supply with respect to the connection part, each of the shuntresistors is provided so as to detect a current flowing in the lowerswitching element of corresponding one of the switching element unitsfor the respective phases, and the inverter control device controls thealternating-current rotary electric machine by PWM control byindividually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases based on alternating-current voltage commands thatare commands for alternating-current voltages of a plurality of phases,performs a current detection process of detecting the currents ofrespective phases flowing in the alternating-current rotary electricmachine based on an electric potential difference between both ends ofeach of the shunt resistors during a lower full-on period in which thelower switching elements of the switching element units for therespective phases are all ON, and reduces a modulation factorrepresenting a ratio of an effective value of the alternating-currentvoltage commands to a voltage on the direct-current side of the inverterwhen the lower full-on period is shorter than a predetermined referencetime.
 14. The drive device according to claim 3, further comprising aninverter control device that controls drive of the inverter, whereineach of the switching element units for the respective phases includesan upper switching element and a lower switching element, the upperswitching element being provided closer to the positive electrode of thedirect-current power supply than a connection part of the switchingelement unit to the alternating-current rotary electric machine, thelower switching element being provided closer to the negative electrodeof the direct-current power supply than the connection part, each of theshunt resistors is provided so as to detect a current flowing in thelower switching element of corresponding one of the switching elementunits for the respective phases, and the inverter control devicecontrols the alternating-current rotary electric machine by PWM controlby individually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases, performs a current detection process of detectingthe currents of respective phases flowing in the alternating-currentrotary electric machine based on an electric potential differencebetween both ends of each of the shunt resistors during a lower full-onperiod in which the lower switching elements of the switching elementunits for the respective phases are all ON, and determines an offsetcorrection amount at a zero point in the current detection process basedon the electric potential difference between both ends of each of theshunt resistors during a lower full-off period in which the lowerswitching elements of the switching element units for the respectivephases are all OFF.
 15. The drive device according to claim 3, furthercomprising an inverter control device that controls drive of theinverter, wherein each of the switching element units for the respectivephases includes an upper switching element and a lower switchingelement, the upper switching element being provided on the positiveelectrode side of the direct-current power supply with respect to aconnection part of the switching element unit and thealternating-current rotary electric machine, the lower switching elementbeing provided on the negative electrode side of the direct-currentpower supply with respect to the connection part, each of the shuntresistors is provided so as to detect a current flowing in the lowerswitching element of corresponding one of the switching element unitsfor the respective phases, and the inverter control device controls thealternating-current rotary electric machine by PWM control byindividually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases, performs a current detection process of detectingthe currents of the respective phases flowing in the alternating-currentrotary electric machine based on an electric potential differencebetween both ends of each of the shunt resistors during a lower full-onperiod in which the lower switching elements of the switching elementunits for the respective phases are all ON, and reduces a carrierfrequency in the PWM control when the lower full-on period is shorterthan a predetermined reference time.
 16. The drive device according toclaim 3, further comprising an inverter control device that controlsdrive of the inverter, wherein each of the switching element units forthe respective phases includes an upper switching element and a lowerswitching element, the upper switching element being provided on thepositive electrode side of the direct-current power supply with respectto a connection part of the switching element unit and thealternating-current rotary electric machine, the lower switching elementbeing provided on the negative electrode side of the direct-currentpower supply with respect to the connection part, each of the shuntresistors is provided so as to detect a current flowing in the lowerswitching element of corresponding one of the switching element unitsfor the respective phases, and the inverter control device controls thealternating-current rotary electric machine by PWM control byindividually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases based on alternating-current voltage commands thatare commands for alternating-current voltages of a plurality of phases,performs a current detection process of detecting the currents ofrespective phases flowing in the alternating-current rotary electricmachine based on an electric potential difference between both ends ofeach of the shunt resistors during a lower full-on period in which thelower switching elements of the switching element units for therespective phases are all ON, and reduces a modulation factorrepresenting a ratio of an effective value of the alternating-currentvoltage commands to a voltage on the direct-current side of the inverterwhen the lower full-on period is shorter than a predetermined referencetime.
 17. The drive device according to claim 4, further comprising theinverter control device that controls drive of the inverter, whereineach of the switching element units for the respective phases includesthe upper switching element and the lower switching element, the upperswitching element being provided on the positive electrode side of thedirect-current power supply with respect to the connection part of theswitching element unit and the alternating-current rotary electricmachine, the lower switching element being provided on the negativeelectrode side of the direct-current power supply with respect to theconnection part, each of the shunt resistors is provided so as to detectthe current flowing in the lower switching element of corresponding oneof the switching element units for the respective phases, and theinverter control device controls the alternating-current rotary electricmachine by PWM control by individually controlling switching of theupper switching element and the lower switching element of each of theswitching element units for the respective phases, performs the currentdetection process of detecting the currents of the respective phasesflowing in the alternating-current rotary electric machine based on theelectric potential difference between both ends of each of the shuntresistors during the lower full-on period in which the lower switchingelements of the switching element units for the respective phases areall ON, and reduces a carrier frequency in the PWM control when thelower full-on period is shorter than a predetermined reference time. 18.The drive device according to claim 4, further comprising the invertercontrol device that controls drive of the inverter, wherein each of theswitching element units for the respective phases includes the upperswitching element and the lower switching element, the upper switchingelement being provided on the positive electrode side of thedirect-current power supply with respect to the connection part of theswitching element unit and the alternating-current rotary electricmachine, the lower switching element being provided on the negativeelectrode side of the direct-current power supply with respect to theconnection part, each of the shunt resistors is provided so as to detectthe current flowing in the lower switching element of corresponding oneof the switching element units for the respective phases, and theinverter control device controls the alternating-current rotary electricmachine by PWM control by individually controlling switching of theupper switching element and the lower switching element of each of theswitching element units for the respective phases based onalternating-current voltage commands that are commands foralternating-current voltages of a plurality of phases, performs thecurrent detection process of detecting the currents of respective phasesflowing in the alternating-current rotary electric machine based on anelectric potential difference between both ends of each of the shuntresistors during the lower full-on period in which the lower switchingelements of the switching element units for the respective phases areall ON, and reduces a modulation factor representing a ratio of aneffective value of the alternating-current voltage commands to a voltageon the direct-current side of the inverter when the lower full-on periodis shorter than a predetermined reference time.
 19. The drive deviceaccording to claim 6, further comprising the inverter control devicethat controls drive of the inverter, wherein each of the switchingelement units for the respective phases includes the upper switchingelement and the lower switching element, the upper switching elementbeing provided on the positive electrode side of the direct-currentpower supply with respect to the connection part of the switchingelement unit and the alternating-current rotary electric machine, thelower switching element being provided on the negative electrode side ofthe direct-current power supply with respect to the connection part,each of the shunt resistors is provided so as to detect the currentflowing in the lower switching element of corresponding one of theswitching element units for the respective phases, and the invertercontrol device controls the alternating-current rotary electric machineby PWM control by individually controlling switching of the upperswitching element and the lower switching element of each of theswitching element units for the respective phases based onalternating-current voltage commands that are commands foralternating-current voltages of a plurality of phases, performs thecurrent detection process of detecting the currents of respective phasesflowing in the alternating-current rotary electric machine based on anelectric potential difference between both ends of each of the shuntresistors during the lower full-on period in which the lower switchingelements of the switching element units for the respective phases areall ON, and reduces a modulation factor representing a ratio of aneffective value of the alternating-current voltage commands to a voltageon the direct-current side of the inverter when the lower full-on periodis shorter than a predetermined reference time.
 20. The drive deviceaccording to claim 10, further comprising an inverter control devicethat controls drive of the inverter, wherein each of the switchingelement units for the respective phases includes an upper switchingelement and a lower switching element, the upper switching element beingprovided closer to the positive electrode of the direct-current powersupply than a connection part of the switching element unit to thealternating-current rotary electric machine, the lower switching elementbeing provided closer to the negative electrode of the direct-currentpower supply than the connection part, each of the shunt resistors isprovided so as to detect a current flowing in the lower switchingelement of corresponding one of the switching element units for therespective phases, and the inverter control device controls thealternating-current rotary electric machine by PWM control byindividually controlling switching of the upper switching element andthe lower switching element of each of the switching element units forthe respective phases, performs a current detection process of detectingthe currents of respective phases flowing in the alternating-currentrotary electric machine based on an electric potential differencebetween both ends of each of the shunt resistors during a lower full-onperiod in which the lower switching elements of the switching elementunits for the respective phases are all ON, and determines an offsetcorrection amount at a zero point in the current detection process basedon the electric potential difference between both ends of each of theshunt resistors during a lower full-off period in which the lowerswitching elements of the switching element units for the respectivephases are all OFF.